Phone data/internet for foreigners

Hola! Happy independence day! We just arrived in Uyuni today, my phone is too old to use an eSIM so I need to buy a sim card so i can use internet. How can I do this in Uyuni? Can I just buy one from a convenience store? How do I put money on it - do I need to do it when I buy it or do it online later? I don't know very much Spanish so I'm a bit embarrassed to go into a store and try to figure it out as I go. Thank you for your help, I'm very excited to be here 😊😊